286dc37d1b
Remove `tokenstream::Delimited`. Because it's an extra type layer that doesn't really help; in a couple of places it actively gets in the way, and overall removing it makes the code nicer. It does, however, move `tokenstream::TokenTree` further away from the `TokenTree` in `quote.rs`. More importantly, this change reduces the size of `TokenStream` from 48 bytes to 40 bytes on x86-64, which is enough to slightly reduce instruction counts on numerous benchmarks, the best by 1.5%. Note that `open_tt` and `close_tt` have gone from being methods on `Delimited` to associated methods of `TokenTree`.
For more information about how rustc works, see the rustc guide.